1. Field of Use
The present invention relates to a keyboard coding apparatus which associates coded information to each key of a keyboard. When such key is actuated, such coded information is related to the selected alphanumeric or control character.
2. Prior Art
A keyboard is one of the simplest and most common devices for entering information into data processing systems. Like other input/output devices, a keyboard connects through an interface unit to the central unit of the equipment of which it is part.
Generally, the interface unit, under the control of the central unit, verifies according to a predetermined sequence if a key has been actuated. When the interface unit detects an actuated key, it takes the code representative of the alphanumeric or control character related to such actuated key and provides such coded information as output.
The keyboard and the interface unit generally form a single element or peripheral unit which is physically separated from the central unit. The connection between the keyboard interface unit and the central unit generally occurs through a group of leads or bus.
The leads can be classified into the following groups: a first group of leads which is used to transmit character codes from interface unit to central unit; and, a second group of leads which is used to exchange control signals between the central unit and the keyboard interface unit.
A keyboard interface unit as described above is manufactured by INTEL Corporation in the form of the 8278 Programmable Keyboard Interface integrated circuit chip. Other keyboard interface units are the subject of numerous patents, as for example, U.S. Pat. Nos. 4,222,038 and 4,106,011.
However, both the use of the keyboard interface circuits of the above mentioned U.S. patents and the use of the 8278 Programmable Keyboard Interface increase substantially the total cost of the equipment of which the keyboard is part. Besides, both the keyboard interface units of the above mentioned U.S. patents and the 8278 Programmable Keyboard Interface require a large number of leads to be connected to the central unit for exchanging data/commands/control signals.